Friday, November 28, 2014

5-10 cm of snow on the way for Winnipeg

Get those shovels ready.. snow is on the way across much of southern Manitoba today into tonight as a storm system over Montana tracks into the Dakotas. Snow from this system has spread into western Manitoba this morning and will continue to spread eastward into Winnipeg and the Red River valley this afternoon. Snow will pick up in intensity by the afternoon rush hour, with 2 cm possible by evening. Snow will continue tonight into Saturday morning with another 5 cm possible in Winnipeg by the time it tapers off by midday Saturday. In total, about 5-10 cm of snow is possible across Winnipeg and the northern RRV, with less to the south of Winnipeg and more to the north. Heaviest snowfall for this system is expected over western MB Parklands and central Interlake regions (Riding Mtns, Dauphin, Arborg, Ashern, etc) where 15-20 cm is forecast by Saturday. In behind this system, winds will shift into the northwest Saturday tapping cold Arctic air once again, with temperatures falling from morning values of -10C towards -20C by Saturday evening. Cold but dry weather is on tap for Sunday and Monday with a moderating trend the rest of the week as the arctic airmass relaxes its grip over southern MB.

16 comments:

About 2 or 3 cm in this first batch of snow this evening.. but looks like snow will taper off or stop for awhile overnight with very little snow evident on upstream Foxwarren radar. However, another batch of snow is spreading over southern SK through the Regina and Moose Jaw areas, and that area of snow should be pushing into YWG/RRV by morning when we should pick up another 2 to 4 cm Saturday morning before it ends Saturday afternoon.

I think we'll get close to -30C, but we won't hit it.. more likely around -28C or -29C. We have a west wind this evening that will keep the temperature from falling too quickly this evening, then the flow becomes SW overnight which saves the airport from getting much colder than guidance.

Tomorrow will be a good example of how misleading windchill values can be. Tomorrow morning, Winnipeg will be around -27C with a 15 km/h wind that will produce a "windchill" of -38 or so. By 5 pm, the temperature will be around -18C, with a brisk south wind of 40 gusting to 60 km/h that will produce a windchill of -31, supposedly not as bad as the morning windchill. But I guarantee that 40G60 km/h wind with -18C temps will feel a lot worse than the 15 km/h winds at -27. It just goes to show you that windchills require wind to be truly representative, and it's misleading and inaccurate to give windchill values with light wind speeds.

November at Winnipeg airport finished with an average temperature of -8.8C, which is about 4C below normal. Going back to 1872, that makes it the 22nd coldest November on record in Winnipeg, and the coldest since the brutal November of 1996 (-11.9C) Last November had an average temperature of -6.0C, so November this year has been colder than last year's. That doesn't necessarily mean the rest of the winter will be colder than last year.. but we are off to a colder start.

So November 2014 was Winnipeg's 22nd coldest Nov on record (since 1872). Looking at the top 25 coldest Novembers on record here, 17 (68%) were followed by a colder than normal December, 3 (12%) were near normal, and 5 (20%) were warmer than normal. The average of those 25 Decembers was -15.8C, or about 2.5C below our current 30 year Dec "normal" of -13.2C. So if history is our guide, then it looks like December will finish below normal, which probably doesn't come as a big surprise. But there is a slight glimmer of hope (20%) that things could turn around this month. We can only hope.. That being said, things look milder for the first half of December especially by the second week (latest CPC 8-14 day outlook looks positively glorious for the Prairies!), so that will be a nice break from the cold if that pans out..

Much nicer day out there than yesterday thanks to much lighter winds and sunshine today. Airport is overdoing wind chill at -24 as of 11 am. with a measly 9 km/h wind. The Forks will be a better gauge of what it really feels like out there today. Windchill not really a factor today! (especially compared to yesterday!)

Was reading a post on another weather discussion forum, and one long range expert was comparing this upcoming winter to that of 1965-66 for North America in terms of similarities to current ENSO set-up and blocking pattern signals. The winter of '65-66 was a severe winter in Winnipeg and southern MB. After a relatively mild and tranquil December, a 30 cm snowstorm on Dec 30-31 ushered in the second coldest January on record in Winnipeg with a monthly average of -26.7C (10C below normal!!). That was followed by a vicious cold snap in mid-February that saw actual air temperatures drop to -45C in Winnipeg (not wind chill!) before a major blizzard on March 4th dumped 35 cm of snow on the city together with 110 km/h gusts that created drifts of 3-4 meters and paralyzed the city and much of the RRV. Now obviously that doesn't mean we'll get a repeat this winter.. but it does show you the potential extreme winter weather we *can* have with another blocking pattern likely setting up this winter together with a moderate El Nino developing out west. Will keep you posted if I hear any updates..

Right now, model consensus is calling for perhaps a dusting of light snow in Winnipeg on Sunday as a warm front crosses southern MB. Other than that, snow chances look minimal over the next week or so.